Bacillus subtilis genes have been cloned in the lambda vector Charon 4A and the identity of the cloned pieces has been verified by means of transformation into B. subtilis. Several libraries have been constructed in this manner using either partial EcoRl fragments of B. subtilis chromosomal DNA or by partial methylation of B. subtilis chromosomal DNA followed by complete EcoRl digestion. Libraries prepared in the latter manner were found to be a more nearly representative random collection of B. subtilis chromosomal fragments than partial EcoRl digests. Several Charon 4A phage have been isolated in pure form that carry regions of the chromosome containing sporulation genes. These fragments are being used to isolate flanking sequences containing other spoulation genes. Cloned sporulation genes used to study the genetic organization of sporulation loci and for studies of transcription of these loci in sporulation mutants. It is anticipated that the cloned genes will allow a significant purification of messenger RNA for sporulation genes which should allow an assessment of the role of translation control in this process.